The invention relates to an aluminum base bearing alloy and a bearing element comprising a running layer formed by the alloy.
In order to avoid the disadvantages of silicon-containing aluminium-tin alloys in view of a lower fatigue strength due to the stress concentration of the silicon particles on the one hand and the chip-removing effect of the silicon particles in the area of the bearing surface on the other hand, the addition of silicon to the alloy is frequently omitted. In order to improve the mechanical properties of silicon-free aluminium alloys with a high tin content of 35 to 65% by weight, it has already been proposed according to DE-A1-42 31 862 A1, in addition to 0.1 to 1.5% by weight of copper in order to improve the fatigue resistance on the one hand, to add to the alloy on the one hand lead and bismuth in an overall quantity of 0.5 to 10% by weight, other hand at least one of the elements manganese, nickel, silver, magnesium, antimony and zinc in an overall quantity of a maximum 5% by weight. Due to the high tin content however, upon hardening of the alloy from the melt, there is formed a substantially coherent tin network, which considerably impairs the structural strength of the plain bearing material and its capacity for shaping, which is of importance with a view to the conventional plating of these cast alloys with steel, and of the shaping stages involved therewith. In addition, as the tin content increases, the network structure of the tin in the aluminium matrix has an increasing influence on the mechanical properties of the plain bearing material.
Attempts have also already been made to improve the mechanical properties of aluminium-tin alloys by adding to these alloys well-known matrix-reinforcing elements such for example as copper, manganese, nickel, magnesium and tin. Such aluminium-tin alloys are known among others from DE 42 01 793 A.
Furthermore it is already known, according to DE 32 49 133 C2, to generate a heterogenous structure in aluminium-tin alloys by means of a thermal aftertreatment. By means of this aftertreatment hard particles, e.g. silicon or aluminides, are separated, enabling favourable wear properties with quite specific distribution functions.
In the case of cast alloys, according to DE-C2-36 40 698, it is necessary in order to establish the final dimension of the individual layers with shaping during the plating with steel, to undertake various shaping stages, which also require various connected thermal treatments. This compound production and in particular the various shaping stages have until now prevented the use of strength-increasing alloying measures.
A layer material for plain bearing elements with a tin content of between 0.5% by weight and 20% by weight is known from DE 40 04 703 A1. By means of the addition of nickel and manganese an attempt is substantially made to produce manganese-containing hard particles in order to improve the wearing properties of such a plain bearing element. A disadvantage here is however that, despite the addition of elements forming hard particles, the tin content remains restricted to up to 20% by weight.
Finally, DE 43 32 433 A1 describes a multilayer plain bearing with a bearing alloy layer on a basis of aluminium and tin. Here also the tin content of the aluminium alloy for the bearing alloy layer is restricted to 20% by weight, and the attempt is made to improve the strength properties of such an aluminium-tin alloy by adding to the alloy elements forming hard material.
The object underlying the invention is to provide an aluminium alloy whose mechanical properties are clearly better, even at higher tin contents.
The object is achieved with an Al base bearing alloy with an alloy matrix consisting of 16 to 32 wt-% Sn as a main alloy component, at least 1.4 wt-% Cu, at least two elements selected from a first element group consisting of Mn, Ni and Fe in a quantity of between 40% and 200% of the Cu quantity, and at least one element selected from a second element group consisting of Cr, Co, Zr, Mg, Sb, W, Nb, V and Mo, the alloy matrix containing 0.1 to 1.5 wt-% Cr, at least 0.2 wt-% of a total of Cr, Co and Zr, this total being at most 200 wt-% of the Fe and Ni content, 0.1 to 1 wt-% of a total of Zr, Mg, Sb, W, Nb, V and Mo, the ratio of Co to Fe in the alloy matrix being 1:1 to 0.2:1, and the remainder being Al with the usual impurities, wherein the elements of the first and second element groups form approximately spherical or cuboid aluminide grains in a proportion, by volume, of from 0.15% to 5% of an interrupted Sn-network structure, the aluminide grains having a maximum of 70% of the average circumferential length of the visible matrix grain boundaries, and at least 15% of the Sn grains being present in a size ratio of 1:1 to the aluminide grains.
Also of advantage is a bearing consisting of a steel support layer, a running layer formed by the above-described Al base bearing alloy, and an intermediate layer between the steel support and running layers.
The amount of Zr in the alloy matrix is 0.1% to 1.0 wt %, preferably between 0.15% and 0.5 wt %. The weight proportion is a maximum 10% for an element of the third element group of Pb, Bi, Cd and In.